The present invention relates generally to hermetic sealing systems and more particularly to a fluidtight seal assembly which is mechanically actuated, expandable, annular, and reusable.
In numerous industries, such as nuclear, manufacturing, and aerospace, certain operations and products require use of an annular expandable hermetic seal between two stationary and flat containment surfaces. Usually the annular seal surrounds an orifice or opening in one or both of the containment surfaces. A simple example would be the use of an expandable annular seal between the sealing flanges of two stationary pipe sections. A more sophisticated example would be the use of an expandable annular seal between the surfaces surrounding the access port valves of a nuclear reactor and a nuclear fuel assembly transfer machine.
Existing annular expandable seals have been only inflatable seals which can be visualized as resembling a bicycle tire innertube which is pumped up with air to achieve a hermetic barrier between two containment surfaces and around any possible opening in each containment surface.
Inflatable seals historically have been used as pressure containment boundaries in a variety of industrial, military, and most recently, nuclear applications. The pneumatic seal concept was initially used to provide seals for aircraft canopies, submersible tank turrets, and airlock doors. They were later incorporated into more critical components such as shield plugs and valves where the seal requirements increased from that of maintaining a pressure controlled environment to that of preventing the loss of minute amounts of radioactive gases.
Inflatable (gas actuated) seals in current use have problems in the areas of cross-seal leakage, range of containment pressure, actuation/deactuation control, service life, and sustained fail-safe operation. Inflatable seals are limited to low inflation pressures, and hence can only contain low pressures between the containment surfaces. The loss of inflation gas from inflatable seals typically is on the order of one to five psi per day. This severely limits the duration a seal can maintain a seal barrier in the event of a failure in the gas or electrical supply system. Increased inflation pressures will increase inflation gas leak rates. Inflatable seals are deactuated by venting the inflation gas to the atmosphere, or in the case of radioactive gas to a gas processing system. There is no indication, or assurance, that the translating portion of the seal has not stuck to the closure sealing surface. The actuation/deactuation of the inflatable seal depends on the reliability of electrical or pneumatic systems to operate or maintain. Also, there has not been a practical method developed yet for detecting defects at the internal surfaces once the inflatable seal has been molded into its inner-tube shape.